2021 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/90484

Proceedings for the 2021 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Thirty-second Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, was held on August 2-4, 2021. For the first, and hopefully the last, time, the meeting was held virtually. At the time of the conference, Texas and the United States was at the height of the initial Delta COVID-19 variant surge. There were 465 registrants from 16 countries, including 167 students. The total number of oral and poster presentations was 403. The meeting consisted of a Monday morning plenary, 56 parallel technical sessions and a poster session. The organizers provided opportunities for networking and live interaction. There were a number of advantages to the virtual format, including elimination of parallel session time conflicts and reduced meeting cost. However, the consensus was that the in-person meeting format is strongly preferred.

The recipient of the 2021 International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Joy Gockel from the Colorado School of Mines. Dr. Ola Harrysson from North Carolina State University won the International Freeform and Additive Manufacturing Excellence (FAME) Award. There are 140 papers in this conference proceedings. Papers marked “REVIEWED” in the title area were peer reviewed by two external reviewers. We have sequentially numbered the pages of the papers to facilitate citation. Manuscripts for this and all preceding SFF Symposia are available for free download below and at the conference website: https://www.sffsymposium.org/; select the “Proceedings Archive” pull-down menu item.

Thirteen materials-related papers were selected as best papers for inclusion in the journal JOM under the aegis of The Minerals, Metals & Materials Society (TMS). Five of these papers were substantially improved for the journal with the original also appearing in this proceedings. Eight were moved with only minor modification; these do not appear in the proceedings. The abstracts of these eight papers appear in the proceedings with a note referring the reader to the JOM full article. These thirteen outstanding papers are notated in the Proceedings Table of Contents and were published in the March 2022 issue of JOM.

The editors would like to thank the Organizing Committee, the session chairs, the attendees for their enthusiastic participation, and the speakers both for their significant contribution to the meeting and for the relatively prompt delivery of the manuscripts comprising this volume. We are grateful to TMS conference management staff for their significant contributions to the meeting planning and proceedings production, particularly Trudi Dunlap, Jennifer Booth and Kelcy Marini. We look forward to the continued close cooperation of the additive manufacturing community in organizing the Symposium. We also want to thank the National Science Foundation (CMMI-2005490) for supporting this meeting financially by providing 161 student registration fee waivers. The meeting was organized within the Mechanical Engineering Department and the Center for Additive Manufacturing and Design Innovation (CAMDI) at The University of Texas at Austin. The 2022 SFF Symposium is planned to be in person on July 25-27, 2022 at the HiltonAustin Hotel inAustin, Texas USA. The conference website will become active in mid-January 2022.

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Investigation of the Properties of Reinforced IN718 Structures Fabricated using Laser Powder Bed Fusion
(University of Texas at Austin, 2021) Ravichander, B.B.; Farhang, B.; Ganesh-Ram, A.; Hanumantha, M.; Ramachandra, S.; Shinglot, Y.; Amerinatanzi, A.; Shayesteh Moghaddam, N.
Inconel 718 (IN718) superalloy, known for its high strength and corrosion resistant behavior, is widely used in the aerospace and automotive industries. Laser power bed fusion (LPBF), one of the commonly used techniques of additive manufacturing, enables the fabrication of structures with a variety of local properties. Using the same material, components with spatially varying properties can be fabricated through applying different processing parameters. In this study, IN718 composite structures were fabricated using four types of rod reinforcements with different geometry. A different set of process parameters was used to fabricated reinforcing rods compared to that of the main part. The bonding quality at the interface between the main part and reinforcements was determined by defect analysis on the microstructure results. Also, Vickers hardness test was performed at the interface in order to examine the mechanical properties of the samples. It was found out that a similar level of densification and hardness value, slightly less than the plain sample, can be achieved using helical and arc reinforcing rods. By contrast, significantly lower density and hardness were observed for the sample reinforced by square rods compared to the plain sample.
A Data Integration Framework for Additive Manufacturing Big Data Management
(University of Texas at Austin, 2021) Perišić, Milica; Milenković, Dimitrije; Lu, Yan; Jones, Albert; Ivezić, Nenad; Kulvatunyou, Boonserm
Large amounts of data are generated throughout the entire, AM, part-development lifecycle. Data are generated by various functions within process monitoring, material characterization, equipment status, and part qualification. Hence, data integration and management are critical in streamlining, accelerating, certifying, and deploying these functions. However, achieving that integration and management has several challenges because AM data embodies the four characteristics of Big Data - volume, velocity, variety, and veracity. This paper proposes an AM framework as a foundation for addressing those challenges. In the framework, AM data are streamed, curated, and configured automatically for real-time analysis and batch processing, which increases the effectiveness of archiving and querying that data. The framework also includes a description of the associated AM metadata, which links the various data types and improves browsing, discovering, and analyzing that data. Finally, the framework can be used to derive requirements for standards that enable data sharing.
Initial Development of a Simulation Model of a Radiation-based Print Heating System for Fused Deposition Modeling
(University of Texas at Austin, 2021) Collins, Daniel S.; Turner, Cameron
Fused Deposition Modeling (FDM) has become a standard 3D printing process for thermoplastics. However, the process results in different strength characteristics along each cardinal direction of a part attributed to different bonding times between filaments. The resulting anisotropic characteristics are an obstacle when considering FDM printed parts for mechanical purposes. Work at Arizona State University has demonstrated a method using laser-based heating to achieve improved polymer bonding without loss of dimensional accuracy. In this research we consider the possibilities of reheating the filament via radiative heat transfer to achieve the same outcome. By exploring the approach in simulation and conducting confirmation experiments, we evaluate the ability to increase strength in FDM components by post-deposition controlled radiative heat-transfer.
Physical Modeling: Simulation of Micro-Void Development within Large Scale Polymer Composite Deposition Beads
(University of Texas at Austin, 2021) Awenlimobor, Aigbe; Wang, Zhaogui; Smith, Douglas E.
Short carbon fiber composites are used in large-scale polymer deposition additive manufacturing due to their increased stiffness and strength and reduced thermal expansion and print distortion. While much attention has been given to interlayer properties, less is known about bead microstructure, including the effect that suspended fibers have on porosity. This paper develops a model for single fiber motion in a purely viscous flow that is simulated with a custom finite element fiber suspension analysis. Our fiber simulation is based on Jeffrey’s model assumptions where translational and rotational velocities which zero applied forces and moments are computed. Velocity gradients along streamlines within the flow of polymer melt through a large-scale polymer deposition additive manufacturing flow field serve as input. The pressure distribution around a fiber is computed along the flow path including the die swell expansion at the nozzle exit. The simulation provides insight into micro-void formation within printed beads.
A Triz-Based Analysis of the Fundamental Limits of Fused Filament Fabrication
(University of Texas at Austin, 2021) Weaver, J.M.; Patternson, C.
Each category of additive manufacturing (AM) has specific fundamental limitations bounded by the physics and material properties involved. For example, the speed of fused filament fabrication (FFF) processes is bounded by how quickly thermoplastics can be melted, deposited, and resolidified while retaining material properties and dimensional accuracy. Incremental improvements approaching these theoretical limits will continue to occur, but more radical changes are necessary to completely overcome the current constraints. This paper considers some of the fundamental limits bounding FFF processes and investigates possible avenues for future research to overcome these limits. The framework for this analysis is the “Theory of Inventive Problem Solving” (TRIZ), a formalized problem solving and ideation tool that generalizes design-specific problems into contradicting engineering parameters, then suggests universal design principles based on analogy to solutions in other systems and patents. TRIZ has been used in many fields successfully, including the design of parts to be more manufacturable through AM, but literature on its application to additive manufacturing processes themselves is limited. Two case studies are shared demonstrating how TRIZ-based analysis can lead to radical improvements in FFF and other AM technologies.
Evaluation of a Cyber-Physical Attack Effectiveness in Metal Additive Manufacturing by Selectively Modifying Build Layer Thickness
(University of Texas at Austin, 2021) Carrion, Patricio E.; Graves, Lynne M.; Yampolskiy, Mark; Shamsaei, Nima
To produce functional parts satisfying required functional characteristics, Additive Manufacturing (AM) process maintains a combination of numerous parameters within material-dependent ranges; these include power density, scanning speed, hatch distance, and layer thickness. Unintentional misconfiguration of these parameters is easily detectable as it impacts the entire build. In this paper, however, we consider the case of a deliberate sabotage attack which causes misconfiguration localized to only few strategically selected layers. We propose a method on how such targeted misconfigurations can be executed without hacking into the firmware. Specifically, we altered a build file to mimic localized layer thickness modification by disabling laser beam exposure, while maintaining geometrical and visual part integrity. For two distinct laser powder bed fusion (L-PBF) systems and two metal alloys, we validated empirically the impact of such attack on part quality and demonstrated that it can avoid detection by non-destructive techniques (NDT). The conducted attack illustrates susceptibility of AM to deliberate sabotage attacks and motivates the need of security solutions for this increasingly adopted manufacturing technology.
Investigating the Effect of Heat Transfer on the Homogenity in Microstructure and Properties of Inconel 718 Alloy Fabricated by Laser Powder Bed Fusion Technique
(University of Texas at Austin, 2021) Farhang, B.; Ravichander, B.B.; Ganesh-Ram, A.; Ramachandra, S.; Hanumantha, M.; Hall, W.; Dinh, A.; Amerinatanzi, A.; Shayesteh Moghaddam, N.
Laser Powder Bed Fusion (LPBF) of metallic components is associated with microstructure and inhomogeneity of properties in the fabricated components. In a recent work by the authors, a novel technique of considering a border surrounding the main part during the LPBF fabrication is proposed to address the issue of inconsistency in microstructure across the cross section of LPBF-fabricated parts. This study, on the other hand, aims to investigate the effect of such border on the microstructure homogeneity along the build direction of LPBF-fabricated parts. For this purpose, a cubic sample surrounded by a cubic border was fabricated to control the rate of heat transfer and then improve the microstructure across the cross section. Also, a sample with identical dimensions and the same process parameters was printed without border as a reference to be compared. To investigate the variation of the properties along the build direction, microstructure and hardness results were compared between areas near and away the substrate for both samples. For the area away from the substrate, in both samples, a deeper pool, less surface porosity, and higher Vickers hardness was observed compared to the area near the substrate. It was found out that, regardless of the focused area, the sample fabricated with border possesses deeper pools, higher level of density as well as higher hardness value. However, in term of homogeneity along the build direction, no significant improvement was observed for the sample fabricated with the cubic border.
Powder Reuse Effects on the Tensile Behavior of Additively Manufactured Inconel 718 Parts
(University of Texas at Austin, 2021) Soltani-Tehrani, Arash; Shamsaei, Nima; Surya, Adapa Venkata; Mallory, Jaikp; Ramakrishnan, Ramesh
Inconel 718 (IN718), with a wide range of applications in aerospace industries and good weldability, is a popular powder feedstock in the laser beam powder bed fusion (LB-PBF) additive manufacturing (AM) process. Due to fabrication, handling, and storage costs, powder feedstock is commonly reused several times. Therefore, it is important to understand how the mechanical properties of LB-PBF parts can be affected by powder reuse given that powder characteristics may change after repeated recycling. This study aims to investigate the effect of powder reuse on the tensile properties of LB-PBF IN718 parts. Powder characteristics such as cohesion and compressibility will be quantified in order to shed light on the variations observed in the part performances. In addition, by correlating the state of the reused powder with tensile properties, the most critical metrics for quality aspects in powder reuse will be determined.
A Method of Predicting Powder Flowability for Selective Laser Sintering
(University of Texas at Austin, 2021) Sassaman, D.; Phillips, T.; Beaman, J.; Milroy, C.; Ide, M.
This work investigates a method for pre-screening material systems for Selective Laser Sintering (SLS) using a combination of Revolution Powder Analysis (RPA) and machine learning. To develop this method, nylon was mixed with alumina or carbon fibers in different wt.% to form material systems with varying flowability. The materials were measured in a custom RPA device and the results compared with as-spread layer density and surface roughness. Machine learning was used to attempt classification of all powders for each method. Ultimately, it was found that the RPA method is able to reliably classify powders based on their flowability, but as-spread layer density and surface roughness were not able to be classified.
Numerical Predictions of Bottom Layer Stability in Material Extrusion Additive Manufacturing
(University of Texas at Austin, 2021) Mollah, Tusher; Comminal, Raphaël; Serdeczny, Marcin P.; Pederson, David B.; Spangenberg, Jon
Robocasting and 3D concrete printing are technologies that belong under the umbrella term material extrusion additive manufacturing. These two free form fabrication methods are used to produce 3D structures/components in materials such as ceramic pastes, thermosets, and concrete. Common for the materials is their viscoplastic behavior during deposition and structural buildup (i.e., increase in yield stress) after deposition. The material’s complex nature makes it a nontrivial task to ensure that printed layers do not deform when depositing additional layers on top. In this paper, we numerically investigate the influence of the yield stress buildup of viscoplastic materials on the stability of the bottom layer during multilayer printing. Specifically, we have developed a computational fluid dynamics model that applies a scalar approach to alter the yield stress. The novel model provides fundamental knowledge on how to design the material’s rheology, so the bottom layer can withstand both the hydrostatic- and extrusion-pressure.
Effects of Powder Reuse and Spatial Location Dependency on the Powder Characteristics and Defect Structure of Additively Manufactured Ti-6Al-4V Parts
(University of Texas at Austin, 2021) Soltani-Tehrani, Arash; Yasin, Mohammad Salman; Shao, Shuai; Shamsasei, Nima
In laser powder bed fusion additive manufacturing (L-PBF AM), different powder characteristics including particle size and morphology may yield different packing states and thus different defect content in the resulting parts. As the powder is spread by the recoater, the packing state may not be uniform on the powder bed, giving rise to location-dependent part performance. In addition, as the powder is reused (a common practice in AM industry), its characteristics continuously evolve, causing the defect content to change from build to build. This study aims to investigate the effects of powder reuse and part location on powder characteristics as well as the defect structure of the parts. Results indicate powder reuse in an L-PBF system may reduce the number of defects in the as-fabricated parts due to the superior packing state of reused powder. Part density was also found to be location-dependent, with more defects near the gas outlet.
Design and Implementation of Laser Powder Bed Fusion Additive Manufacturing Testbed Control Software
(University of Texas at Austin, 2021) Yeung, Ho; Hutchinson, Keely; Lin, Dong
The National Institute of Standards and Technology developed a facility titled the Additive Manufacturing Metrology Testbed to advance the research in laser powder bed fusion (LPBF) processes. The testbed adopted an open control architecture which allows full access to all key process parameters. Although LPBF control is a very important topic, very little literature can be found on how this is implemented. This paper reviews the testbed control software design and implementation. Scan path planning, galvo motion control, and laser power control are detailed with select highlights. Comparison with commercial machine control software is made, and recent experiments utilizing the advanced features of the testbed control software are also discussed.
On the Diminishing Returns of Thermal Camera Resolution for PBF Temperature Estimation
(University of Texas at Austin, 2021) Wood, Nathaniel; Schwalbach, Edwin; Gillman, Andrew; Hoelzle, David J.
Powder Bed Fusion (PBF) faces ongoing challenges in the areas of process monitoring and control. Standard methods for alleviating these issues rely on machine learning, which requires costly and time-consuming training data. Expense is compounded by the perceived necessity of using sensors with extremely high resolutions. This research avoids this cost by employing an Ensemble Kalman Filter (EnKF), which uses measured data to correct physics-based model predictions of the process, to monitor part internal temperature fields during building. This work tests EnKF performance, in simulation, for two model architectures, using simulated cameras of varying resolution as our measuring instruments. Crucially, we show that increasing camera resolution produces diminishing returns in EnKF accuracy, relative to the model predictions, with up to 81% error reduction. This result shows that current AM quality control practices with expensive sensors may be inefficient; with appropriate algorithms, cheaper setups may be used with little additional error.
Configuration Control for Additive Manufacturing Digital Twins
(University of Texas at Austin, 2021) Gibbons, D.W.; Ko, H.
The additive manufacturing workflow is a ductile entity, often varying depending on the design, the product, the process, the material, and the application. Information models and schemas have been developed that can provide structure to data and information throughout the workflow. The result has been a well-characterized outline of an additive manufacturing digital thread. However, implementation-specific details are often missing from these characterizations, creating challenges in establishing part-specific workflows necessary for product configuration control and management. While software vendors are increasingly filling this gap, a software-agnostic workflow is yet to be defined. This paper investigates the additive manufacturing workflow and establishes the fundamentals of a standardized, configuration-control approach including formats and interoperability while addressing versioning, digital rights, and ownership.
Effects of Local Fiber Orientation State on Thermal-Mechanical Behaviors of Composite Parts Made by Large Area Polymer Deposition Additive Manufacturing
(University of Texas at Austin, 2021) Wang, Zhaogui; Fang, Zhenyu; Smith, Douglas E.
Short carbon fiber enhances the dimensional stability and material strength of composite parts created via large area polymer deposition additive manufacturing, which has been used for rapid fabrications of large-dimension composite parts and tooling. Nevertheless, the flow-induced fiber orientation formed during the material extrusion and deposition leads the deposited composites exhibit non-homogeneous thermal-mechanical behaviors. This study evaluates the fiber orientation state of a 20 wt.% CF-PEI composite fabricated by polymer deposition using the fully coupled flow/orientation approach. The material properties are computed by considering the deposited bead as heterogeneous segments with different local fiber orientation states. The heterogeneous thermal conductivity and expansion coefficient exhibit maximum local differences of 29% and 21%, respectively. The orientation-homogenized material properties are implemented to the finite element simulation for a large area additive manufacturing process of a single bead and notable differences are seen between results computed by employing the homogenous and heterogeneous properties.
Review of Current Problems and Developments in Large Area Additive Manufacturing (LAAM)
(University of Texas at Austin, 2021) Crisp, Tyler G.; Weaver, Jason M.
Large Area Additive Manufacturing (LAAM), also known as Big Area Additive Manufacturing (BAAM), is a screw extrusion, pellet-fed additive manufacturing technology. The large build area, rapid build speed, and inexpensive pelletized feedstock of LAAM are major advantages over conventional AM methods. LAAM has a large variety of applications in areas including energy, automotive, aerospace, high volume production, and composite molds. However, LAAM is not without its challenges. The largest challenges LAAM faces include mechanical properties, uniformity and precision, and predictability of composite material properties. The goal of this paper is to present current research regarding challenges in LAAM, methods of addressing those challenges, developments, and applications, as well to highlight further research to be done.
Effect of Process Parameters on the Vibration Properties of PLA Structure Fabricated by Additive Manufacturing
(University of Texas at Austin, 2021) Xue, Fangkai; Robin, Guillaume; Boudaoud, Hakim; Cruz Sanchez, Fabio A.; Daya, El Mostafa
Advances in Fused Filament Fabrication (FFF) enable the design and manufacturing of multi-material and multi-functional structure that can potentially be used to develop light weight and high damping structures for vibration control. However, very few studies mention the vibration characteristics of FFF printed structures. This paper investigates the effect of four process parameters, raster angle, nozzle temperature, layer height and deposition speed, on the vibration properties of FFF printed Polylactic Acid (PLA) structure through modal analysis and design of experiment. The effects of all four parameters show a good agreement on the first fives modes of resonance. It was found that raster angle significantly affects both resonance frequency (16.6%) and loss factor (7.5%). Meanwhile, the impact of the other three parameters is relatively low (less than 4%), which is different from previous research results on static mechanical properties. All these results provide a guidance for further application of FFF in vibration field.
Bimetallic Castings for Wear Performance through Infiltration of Additive Manufactured Metal Lattice Structures
(University of Texas at Austin, 2021) Liggett, J.C.; Snelling, D.A.; Xu, M.; Myers, O.J.; Thompson, S.M.
High chromium white iron is an alloy frequently employed in the production of abrasion resistive wear components. Ground engaging components for mining or earthmoving frequently require such materials, as well as slurry pumps for mining applications. Although high chromium white iron alloy demonstrates excellent wear performance due to the formation of chromium carbides, it is brittle and lacks toughness. Impact resistance is often of great importance for ground engaging wear components; hence, this study will investigate a method by which high chromium white iron wear components may be reinforced by the formation of a bimetallic composite. In this research, an additively manufactured lattice structure of 316L stainless steel is infiltrated with high chromium white iron via the metal casting process. This procedure results in a bimetallic casting of reinforced white iron. Complete infiltration and metallurgical diffusion bonding were observed between the two alloys, validating this method as a means of reinforcing high chromium white iron castings for applications requiring high abrasion and impact resistance.
Automated Anomaly Detection of Laser-Based Additive Manufacturing Using Melt Pool Sparse Representation and Unsupervised Learning
(University of Texas at Austin, 2021) Zhao, Xiyue; Imandoust, Aidin; Khanzadeh, Mojtaba; Imani, Farhad; Bian, Linkan
Advanced thermal imaging is increasingly invested in direct energy deposition (DED) additive manufacturing (AM) to cope with information visibility of melt pool and tackle process inconsistency. However, there are key challenges regarding the feasibility of current image-guided monitoring methodologies in the DED process. First, high-resolution thermal images consist of millions of pixels captured by hundreds of frames lead to the curse of dimensionality in analysis. Second, the presence of various exogenous noise, ill-structured data, and significant cluster imbalance limit the capability of the current methodologies to perform real-time monitoring. The objective of this research is to advance the frontier of melt pool monitoring in DED process by designing an automated and unsupervised anomaly detection on high-dimensional thermal image data. Specifically, we develop a variational autoencoder to generate a low-dimensional representation of each input thermal image data. A Gaussian mixture model and K-Mean clustering are integrated with the generative model to split latent space into homogenous regions and detect anomalies. Experimental results show that the proposed methodology is highly effective in detecting defective melt pools with accuracy up to 94.52% and a false alarm rate of less than 2.1%.
Evaluation of Liquid Doping Methods for Use in Laser Powder Bed Fusion
(University of Texas at Austin, 2021) Davis, T.M.; Crane, N.B.
Laser powder bed fusion (LPBF) is an additive manufacturing (AM) process that is well known for its geometric versatility and high-quality parts. While the properties of LPBF parts are commonly superior to those made using other AM techniques, LPBF is generally limited to a single material in any given build. While LPBF can accommodate the integration of multiple components into a single part geometrically, the material limitation leads to over-designing to ensure that every component can complete their various functions. Some studies have shown potential methods of 3D composition control throughout a part, but these methods are subject to high cost increases due to build time increases and decreased powder recyclability. A new approach to multi-material LPBF uses liquid dopants to alter the composition in location-specific areas. The current study evaluates two different liquid deposition methods – direct write and inkjet deposition – in relation to their adaptability and utility in LPBF. Inkjet deposition is shown to have significant benefits compared to the direct write method.

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